Sialidosis type 2 (acid neuraminidase deficiency): clinical and biochemical features of a further case

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Abstract
A further patient with a presumed primary deficiency of sialidase (N-acetylneuraminic acid hydrolase, EC 3.2.1.18) is described. Clinically the patient falls into the sialidosis type 2 category of the recent classification of Lowden and O''Brien (1979), i.e., he manifests coarse facies, mental retardation and skeletal changes of dysostosis multiplex as well as myoclonus and a cherry-red spot at the macula. Sialidase activity in fibroblasts was 4% of control values using a methylumbelliferone substrate. The father of the patient had 50% activity. Abnormal amounts of sialyloligosaccharides were found in the urine. The electrophoretic mobility of known glycosylated enzymes and proteins was altered (more anodal than usual), but could be corrected by incubation of the cell extracts with bacterial neuraminidase. The relationship of the present patient to the Lowden and O''Brien classification is discussed.